1. Field of the Invention
This invention is a method for recovering petroleum from subterranean petroleum-containing formations. More particularly, this concerns a method for recovering viscous, asphaltic or bituminous petroleum from formations containing same, including tar sand deposits. Still more particularly, this invention concerns a method whereby surface active agents are generated in situ in the bituminous or asphaltic petroleum by contacting the labile groups associated with the petroleum molecules with an oxidizing gas to activate the group followed by contacting the oxidized groups with an alkalinity agent such as ammonia gas.
2. Description of the Prior Art
Petroleum is recoverable from subterranean formations in which it has accumulated only if certain essential elements co-exist; namely, the formation must have adequate permeability or interconnected flow channels so that a fluid will flow from one portion of the formation to the other; the petroleum viscosity must be sufficiently low that it will move if the flow channels exist and a pressure differential is applied to the fluids; and finally, a source of energy to provide the pressure differential to induce the fluid movement must exist naturally or be supplied to the formation. When all three of these conditions co-exist, so-called primary recovery in which fluid moves to the surface under its own initiative without any type of formation treatment is possible. Supplemental recovery is necessary when any of these basic elements is missing or when the energy has been depleted through primary recovery, and frequently it is necessary to take corrective measures for both petroleum viscosity and simultaneously supply fluid drive energy.
The most extreme examples of formations requiring substantial treatment in order to induce the flow of petroleum therefrom are the so-called bituminous sands or tar sands deposits. Extensive tar sand deposits are found in the western United States, in northern Alberta, Canada, and in Venezuela, and lesser deposits are located in Europe and Asia. The Athabasca deposits in Alberta, Canada, are the most famous, and it is estimated that these deposits contain as much as 700 billion barrels of petroleum. Some production has been obtained from the near surface deposits by strip mining, but essentially no commercial production has been obtained from deep subterranean deposits for several reasons. The fluid permeability of tar sand deposits in their initial state is extremely low, and the viscosity of petroleum at formation temperatures is in the range of millions of centipoise. Accordingly, substantial treatment would be necessary to reduce the high petroleum viscosity so as to achieve petroleum flow under the influence of externally applied drive pressure, and the low permeability of the formation interferes with any such treatment.
Several methods have been described in the literature for recovering bituminous petroleum from tar sand deposits. One of the more popular processes is referred to as a steam emulsification drive process. The first step involves establishment of a high permeability communication path, preferably in or near the bottom of the tar sand deposit, extending from one well to another. Steam and a minor amount of a caustic substance such as sodium hydroxide is introduced into the communication path and flows to the other well. An oil-in-water emulsion is formed, the bituminous petroleum comprising the discontinuous phase of the emulsion. The viscosity of this emulsion is in the range of only a few centipoise, and so it readily moves to the production well for recovery to the surface. Numerous problems have been encountered in actual application of this process, however, including lower than desirable concentrations of bituminous petroleum in the produced emulsion, and the production of a portion of the petroleum in the form of a water-in-oil emulsion which is more viscous than the free bitumen and which resists resolution into its separate phases by demulsification technology. In addition, the communication path is difficult to establish.
Other processes have been described such as in situ combustion as well as various modifications of solvent extraction processes. In commonly owned co-pending applications Ser. No. 481,581 and 481,582 both filed June 21, 1974, a low temperature, controlled oxidation process is described. This process appears more applicable to the low permeability tar sand deposits than does the high temperature in situ combustion reaction.
In view of the foregoing discussion, it can be appreciated that there is a substantial, unfulfilled need for a method for in situ separation of bituminous petroleum from tar sand deposits which can be conducted in the deposits which are too deep to be exploited by means of strip mining. There is an especially acute need for an economical method for extracting a reasonably high percentage for the petroleum contained in these deposits. There is an especially serious need for a method for recovering bitumen in the form of an oil-in-water emulsion under conditions which will exclude the formation of a water-in-oil emulsion. There is similarly an unfulfilled need for a method for increasing the concentration of bitumen in the oil-in-water emulsion produced during the steam-emulsification drive process.